Tal 100rs : big deception

[Erathostene]

I bought a few month ago a tal 100RS. After a few observations, I noticed that I lose many contrast when a bright object at the center. The image can be beautiful and contrasting but when the object (like Saturn) is in the center, image becomes low contrasted. After trying to understand the phenomenon, I found that there were many more diffusion in centre (with all eyepieces). I thought chromaticism was involved, but thebut the low contrast would be in the whole field and not just the center. It's when the objetc is the the brightest that the lost of contrast can be detected. So I examined the lens with a strong light, and I have just realized that there were many little scratches. In addition there are traces of cleaning INSIDE. Then, I think that lost of contrast is done by a strong diffusion in center caused by scratches.

I don't know if the problem is from Russia or from German dealer, but I have waited too long to return the glasses and get a refund. 300 euros for an instrument that can be used only for the moon is high price to pay. Big deception. Luckily I also have a newton.

[John]

That must be very disappointing after a long wait to get the scope. I would definitely get the dealer to supply a replacement though and at no expense to you. The scope you have been supplied with clearly has damaged optics. They should be pristine, assuming it was sold as a new scope.

[NGC 1502]

Was this bought by yourself as a new telescope ?

In the UK, and if you are certain that the scope had problems that were there at purchase, then many dealers would sort out the issue, even if the scope had been purchased a while back.

I'd contact the supplier, and see if the problem can be resolved.

If the scope was second hand, it's a different story. Morally, the seller should have mentioned the scratches, but it could be hard to get a refund, if they are not willing.

Hope you find a solution, Ed.

[KaStern_Former_Member]

Salut Erathostenes,

c'est dommage.

Excessive strailight because of many scratches is not normal.

The sample you bought might be a used refractor wich has been sold to you as new.

You should call the dealer and claim for a refund.

Cheers, Karsten

[Erathostene]

I will try again to contact, but I have few illusions. The seller is not in the same country as me, and I didn't see the problem immediately: scrtchess are visible only with a strong light (we call it "filandre" in French, I haven't the english word for those scratches wich are only visble with a strong light), and with the bad weather It was impossible to do a good observation to see the problems. Thanks

The fact that the contrast is just collapsing in the center is strange. It is because of this fact, that I initially suspected the cause was the reflections in the eyepieces, but after the constatation of the scratches....

[Moonshane]

is it possible to remove the lens cell to look at the inside face of the objective? that said doing so will probably end the warranty.

[Erathostene]

I try to contact the seller before to do that.

I also try to get a polarizing filter before to remove the lens cell: if reflection in eyepieces are reponsibles, the problem will disappear. If the problem persists, it's the objective which is guilty.

[Jim Steele]

If you get no luck with the original dealer you might be able to use an objective from a second hand 100R?

[nightfisher]

Good luck getting this put right, your TAL100 should give VERY good views

[KaStern_Former_Member]

Hello Folks,

I was not so impressed by the views a 4" f/10 TAL gave.

The aperture is limited and the views are further compromised by visible colour aberration.

I prefer views free from visible colour aberration and with more detail.

Cheers, Karsten

[RobH]

I was not so impressed by the views a 4" f/10 TAL gave.

The aperture is limited and the views are further compromised by visible colour aberration.

I prefer views free from visible colour aberration and with more detail.

Cheers, Karsten

Be fair.

It's a £250 achromat. If you want the above you need to spend quite a bit more money.

I have a TAL100 and consider it good value on the moon and planets for the price. I also have a top line 6 inch triplet apo, and it's a lot better, but cost vastly more.

[KaStern_Former_Member]

Hello Rob,

because of the colour aberration free views I even prefer the TAL 110mm Newt to the TAL achromat.

If I add a bit more aperture like with a 150mm f/5 TAL newt or 150mm f/8 Synta Newt

I get both colour aberration free views and higher resolution.

To be fair I have to say that all these Newts need to be collimated welll

and a user who cannot collimate or does not want to collimate

should better buy a refractor (and hope it will come perfectly collimated).

Of the achromatic refractors I prefer the classical long ones,

like the japanese 80mm f/15 or a 4" f/15 over the somewhat short 4"f/10.

The modern 4" f/9 ED refractors are not very expensive,

but they cost about twice the price of the TAL achromat.

Cheers, Karsten

[John]

Hello Rob,

because of the colour aberration free views I even prefer the TAL 110mm Newt to the TAL achromat.

If I add a bit more aperture like with a 150mm f/5 TAL newt or 150mm f/8 Synta Newt

I get both colour aberration free views and higher resolution.

To be fair I have to say that all these Newts need to be collimated welll

and a user who cannot collimate or does not want to collimate

should better buy a refractor (and hope it will come perfectly collimated).

Of the achromatic refractors I prefer the classical long ones,

like the japanese 80mm f/15 or a 4" f/15 over the somewhat short 4"f/10.

The modern 4" f/9 ED refractors are not very expensive,

but they cost about twice the price of the TAL achromat.

Cheers, Karsten

How does this help the OP with his problem ?

[KaStern_Former_Member]

Hello John,

How does this help the OP with his problem ?

no.

The only thing that helps is to contact the vendor.

But depending on wich dealer sold the the TAL to him it will have no effect at all.

Cheers, Karsten

[Roberto Coleschi]

I got TAL 100 RS, also, and for me, is a good value for money: is heavy, it has a bad focuser, and a yellow dominant due the optical treatment, but is a pleasure to watch through it (despite the limitations, it is not a 140 TEC). I'm sorry for your experience, I hope you reach to contact the dealer for the refund or for a change.

[twotter]

The thread title drew me in as it suggested a negative view of the TAL100RS. My initial interest was in reading a different opinion on the telescope, but what I've found is a reminder to take extra care when checking a new astro purchase. Hopefully the op will get a positive response from the supplying dealer, so they can enjoy their TAL.

[Erathostene]

I've no answer from seller (hollidays?)

But even if there's some scratches visible only with strong light I'm not sure that the refractor is really guilty. The constrast is very good when the object is not exactly at the center of the field. Then reflection in eyepieces when when the brightness is strongest could be the cause. But I've not this probleme with my reflector. Then I don't understand.

[Peter Drew]

I would examine the assembly of the two lens elements, the problem you describe suggests to me that the front element may have been replaced the wrong way round possibly subsequent to cleaning if the telescope is a used one, The front element should have the least curvature facing the sky.

[Erathostene]

I'll try to reverse the lens if the seller don't answer and after a test with a filter ; thanks

[Erathostene]

Test with an ortho. I'm very reassured, the problem is no longer therewith a such eyepiece: and the picture is really nice contrasted. I Think It was just a ghost image problem due to bad eyespieces.

[Marki]

That is good news. I have a 100RS - it is a great scope, excellent for its price. Hopefully you will have some great fun with it .

[Erathostene]

With a correct eyepiece I've seen the quality : good contrast, little chromatism, then I've bought a astro Hutech to have my own ortho to enjoy the qualities of my refractor (the little scratches are apparently not a problem)

[Jim Steele]

Glad you managed to sort it, tal scopes do have a reputation for their solid construction

[Erathostene]

A night without turbulence, a good eyepiece (ortho astro hutech 9mm) and it's a real revolution : with an extraordinary eyepiece, I've seen the real capacities of the tal :

-chromatism : at 120x, there's no false colours on moon (first quarte) and saturn. For an achro it's very good.

The contrast is very excellent, and for only 100mm, the details are very good.

I've no more the problem of lose of contrast at centre of the field with this eyepiece.

With the 25mm (tal) and 35mm (baader eudiascopic) I haven't problems but at high and middle magnifications, I had those problems. At middle magnification, the refractor is now pefect. Then I recommand now the tal 100mm after bad begining due to bad plössl eyepieces.

[haitch]

Glad you are sorted. I've only just come across this thread but thought it odd that the surface of the lens was the cause of your problems - I've looked through lenses which were, by the sound of it, much worse than yours and have noticed very little, if any, image degradation.